1. Field of the Invention
The invention relates generally to miniature electromagnetic switches for microwave systems. More specifically, the invention relates to a miniature double-throw electromagnetic switch for operation in microwave or millimeter wave frequencies.
2. Description of the Prior Art
Switches are basic building blocks of communication electronics and are widely used for telecommunications applications such as signal routing, redundancy switching, impedance matching networks and adjustable gain amplifiers. Mechanical relay, PIN diode and FET are the common microwave switches. Mechanical relays offer the benefits of low insertion loss, large off-state isolation, high linearity and high power handling capabilities. However, they consume a significant amount of power and are bulky, heavy and slow. Semiconductor switches such as PIN diode and FET provide much faster switching speed and smaller size and weight but are inferior in insertion loss, isolation, linearity and power handling capabilities than mechanical relays.
Microwave switches providing the advantageous properties of both the mechanical relay and semiconductor switch are then highly desirable, especially for space, airborne and mobile telecommunications applications. Micromachining technologies promise to enable the fabrication of such switches, i.e., switches with the high microwave performance of mechanical switches but also with the small size, weight and power consumption of semiconductor switches. Furthermore, conventional microelectronics fabrication processes are usually used for micromachining, making the integration of such miniature switches with other active electronics possible.
In U.S. Pat. No. 6,016,092 entitled xe2x80x9cMiniature Electromagnetic Microwave Switches and Switch Arraysxe2x80x9d filed on Aug. 8, 1998 by C. X. Qiu, L. S. Yip and Y. C. Shih, single-pole single-throw micro electromagnetic switches in a coplanar waveguide, a microstrip or stripline form were described. A double-throw switch in a stripline form was also described. More recently, in U.S. patent application Ser. No. 09/400,256 entitled xe2x80x9cDouble-throw Miniature Electromagnetic Microwave Switchesxe2x80x9d filed on Sep. 21, 1999 by the same inventors of the above U.S. patent, double-throw micro electromagnetic switches in a microstrip form and a coplanar waveguide form and with controlled magnetization are disclosed. These single-pole double-throw switches are useful to the fabrication of microwave modules, which require a plurality of switches for operation at microwave or millimeter wave frequencies.
Two schematic views of a prior art of a miniature double-throw electromagnetic switch (20) disclosed in U.S. patent application Ser. No. 09/400,256 entitled xe2x80x9cDouble-throw Miniature Electromagnetic Microwave Switchesxe2x80x9d, filed on Sep. 21, 1999 by L. S. Yip, C. X. Qiu and Y. C. Shih, hereinafter called Double-throw Switch A, are shown in FIGS. 1(a) and 1(b). FIG. 1(a) shows a schematic top view of the Double-throw Switch A (20) and FIG. 1(b) shows the schematic cross-sectional view of the switch (20) taken along line A-Axe2x80x2 in FIG. 1(a). The double-throw switch A (20) is fabricated on a dielectric substrate (21) with a ground plane (22 in FIG. 1(b)) deposited on backside of the dielectric substrate (21). An input microstrip line (23a) and a first output microstrip line (25) are deposited on a front side of the dielectric substrate (21). It is seen that the input microstrip line (23a) and the first output microstrip line (25) are aligned in such a way that a continuous microstrip line can be formed when the two are connected electrically. The input microstrip line (23a) and the first output microstrip line (25) are separated by a gap (24) having a length, (Lg). A first cantilever (23b) with a length (26) is deposited over the gap (24) (see FIG. 1(b)). A layer of permanent magnetic material (27) is deposited on part of the first cantilever (23b). A second output microstrip line (28) having a second cantilever (29) is deposited so that the second cantilever (29) is suspended over the first cantilever (23b). The second output microstrip line (28) may be deposited on the same dielectric substrate (21) with the input microstrip line (23a) and the first output microstrip line (25), or on a different dielectric substrate. The second cantilever (29) overlaps part of the first cantilever (23b) in region without the magnetic film (27) so that when the first cantilever (23b) is pushed upwards, a leading portion of the first cantilever (23b) can make electrical contact with the second cantilever (29). The overlap between the first cantilever (23b) and the first output microstrip line (25) is (36) whereas the overlap between the first cantilever (23b) and the second cantilever (29) is (37). A layer of dielectric material (22xe2x80x2) such as SiO2 or polyimide is applied on the ground plane (22). A miniature electromagnetic coil (30) is deposited or attached to the dielectric material (22xe2x80x2). Width (31) of the input microstrip line (23a) and the first output microstrip line (25) is selected to be substantially equal to the width (32) of the second output microstrip line (28). Values of (31) and (32) are determined by the thickness (33, in FIG. 1(b)) of the dielectric substrate (21), the dielectric constant, and the central frequency of the microwave signals to transmit for low loss operation. The second output microstrip line (28) may be arranged so that it makes an angle of roughly 90 degrees with respect to the input microstrip line (23a) and the first output microstrip line (25).
The operation of the Double-throw Switch A (20) is as follows. When no current is applied to the miniature electromagnetic coil (30) (I=0), no magnetic force is applied to the first cantilever (23b) and the first cantilever (23b) is in a normal position in between the first output microstrip line (25) and the second cantilever (29) of the second output microstrip line (28). When a positive current (I greater than 0) is applied to the miniature electromagnetic coil (30), so that the direction of the magnetic field (Be) induced is substantially parallel and opposite to the magnetic moment (Bm, in FIG. 1(b)) of the permanent magnetic film (27), an attraction force will be caused on the first cantilever (23b). When the current (I) exceeds a pull-down threshold or when the force is sufficiently large, the first cantilever (23b) will be deformed so that the first cantilever (23b), attaching to the input microstrip line (23a), will get in contact with the first output microstrip line (25). Microwave signals applying to the input microstrip line (23a) will be allowed to reach the first output microstrip line (25). Since there is no electrical contact between the first cantilever (23b) and the second cantilever (29), which is connected to the second output microstrip line (28), the incoming microwave signals will not reach the second output microstrip line (28). When the current (I) through the miniature electromagnetic coil (30) is reversed, so that the direction of the magnetic field (Be) induced is substantially parallel and along the magnetic moment (Bm) of the permanent magnetic film (27), a repulsion force will be caused on the first cantilever (23b). When the reverse current (I) exceeds a push-up threshold or the repulsion force is sufficiently large, the first cantilever (23b) will be pushed away from the first output microstrip line (25) and eventually get in contact with the second cantilever (29) connected to the second output microstrip line (28). Microwave signals supplying to the input microstrip line (23a) will not be allowed to reach the first output microstrip line (25). Since there is electrical contact between the first cantilever (23b) and the second cantilever (29), the incoming microwave signals will reach the second output microstrip line (28). It is consequently clear that the Double-throw Switch A (20) requires continuous supply of current (I) to the micro-coil (30) in order to obtain reliable operation, at least for one of the two operation states.
A second miniature double-throw microwave switch disclosed in U.S. patent application Ser. No. 09/400,256 filed on Sep. 21, 1999 by L. S. Yip, C. X. Qiu and Y. C. Shih, hereinafter called Double-throw Switch B, which is related to this invention is shown in FIGS. 2(a) and 2(b). FIG. 2(a) shows a top view of the Double-throw Switch B (70) on a dielectric substrate (71). FIG. 2(b) is the schematic side view of the switch (70) taken along line D-Dxe2x80x2 in FIG. 2(a). The double-throw switch (70) contains a first cantilever (72) and a second cantilever (73). The length of the first cantilever (72) and the second cantilever (73) are chosen to be the same and is given by (26). A first permanent magnetic film (74) is deposited on the first cantilever (72) whereas a second permanent magnetic film (75) is deposited on the second cantilever (73). The first cantilever (72) overlaps part of a first output microstrip transmission line (76) whereas the second cantilever (73) overlaps part of a second output microstrip transmission line (77). Both cantilevers (72, 73) are connected to an input microstrip transmission line (78). Hence one end of the input microstrip transmission line (78) has a first cantilever (72) and the other end has a second cantilever (73). Width (76a) of the first output microstrip transmission line (76) is made to be substantially equal to the width (77a) of the second output microstrip transmission line (77) and the width (78a) of the input microstrip transmission line (78). Values of (76a), (77a) and (78a) for low loss operation are determined by the thickness (84, in FIG. 2(b)) of the dielectric substrate (71), the dielectric constant, and the central frequency of the microwave signals to transmit.
As seen in FIG. 2(b), the overlap between the first cantilever (72) and the first output microstrip line (76) is (86) and the overlap between the second cantilever (73) and the second output microstrip line (77) is (87). The first output microstrip line (76) and the input microstrip line (78) are separated by a gap (88) whereas the second output microstrip line (77) is separated from the input microstrip line (78) by another gap (89). Also seen in FIG. 2(b), a miniature electromagnetic coil (81) is deposited or attach to a dielectric material (82), which is deposited on the ground plane (83).
The operation of the Double-throw Switch B (70) is as follows. Since only one miniature electromagnetic coil (81) is used to actuate the two cantilevers (72, 73), the magnetic polarizations (Bm, Bmxe2x80x2) on the two permanent magnetic films (74, 75) must be different. When the magnetic polarizations (Bm, Bmxe2x80x2) are different, preferably opposite, and with a positive current (I) applied to the miniature electromagnetic coil (81), the magnetic field (Be) created will induce attraction force on the second cantilever (73) and a repulsion force on the first cantilever (72), causing contact of the second cantilever (73) with the second output microstrip line (77) while causing an open between the first cantilever (72) and the first output microstrip line (76). Hence microwave signals incident from the input microstrip line (78) will be allowed to go through the second cantilever (73) to reach the second output microstrip line (77). Since there is no electrical contact of the input microstrip line (78) with the first output microstrip line (76), microwave signals will not be coupled from the input microstrip line (78) to the first output microstrip line (76). When the current (I) applied to the miniature electromagnetic coil (81) is reversed, the magnetic field (Be) from the miniature electromagnetic coil (81) will be inverted to induce a repulsion force on the second cantilever (73) and an attraction force on the first cantilever (72), causing contact between the first cantilever (72) and the first output microstrip line (76) while causing an open between the second cantilever (73) and the second output microstrip line (77). Hence, when the current (1) is inverted, microwave signals incident from the input microstrip transmission line (78) will be allowed to go through the first cantilever (72) to reach the first output microstrip line (76). Since there is no electrical contact between the second cantilever (73) and the second output microstrip transmission line (77), microwave signals will not be coupled from the input microstrip transmission line (78) to the second output microstrip transmission line (77).
Although the Double-throw Switch B (70) may operates at a moderate microwave frequencies, when the first cantilever (72) is actuated to make contact with the first output transmission line (76) the open second cantilever (73) connected to the input microstrip transmission line (78) will act as an antenna and result in unwanted reflection and losses of the incident microwave signals at higher frequencies. This is because the length (26) of the second cantilever can""t be made too small compared with wavelength of the microwaves signal at high frequencies.
The present invention allows the fabrication of miniature electromagnetic double-throw switches based on the micro-machining technologies to minimize RF losses and to increase the RF frequencies of operation. The present invention also allows the switches to have latching mechanism to minimize the power consumption of the double-throw switches.
In one embodiment of this invention, a double-throw miniature microwave switch with a dielectric substrate, an input transmission line, a first movable cantilever and a second movable cantilever each with a permanent magnetic film is provided. Said first movable cantilever forms part of a first output transmission line whereas said second movable cantilever forms part of a second output transmission line. When actuated by a magnetic field in one direction, said first movable cantilever moves downwards to cause contact between said input transmission line and said first output transmission line whereas said second movable cantilever moves upwards to isolate said second output transmission line from said input transmission line. When the direction of said actuation magnetic field is reversed, said first movable cantilever moves upwards to cause an isolation between said input transmission line and said first output transmission line whereas said second movable cantilever moves downwards to cause contact between said input transmission line and said second output transmission line.
In another embodiment, a double-throw miniature microwave switch with recess contact regions is provided. The presence of un-wanted particles on the substrate is unavoidable and those under the movable cantilevers in a switch may increase the contact resistance and reduce the contact pressure. By creating at least one recess contact region for each movable cantilever, the effect of said unwanted particles can be reduced and the contact pressure can be increased to give rise to a reduced contact resistance.
In yet another embodiment, a double-throw miniature microwave switch, having non-symmetrical movable cantilevers and transmission lines with tapered or rounded corners is given. Sharp corners in transition between the input transmission line and the output transmission line are eliminated in this switch to minimize the reflection and losses of propagating microwaves or millimeter waves.
In yet another embodiment, a double-throw miniature microwave switch with latching is given. Said switch consists of a dielectric substrate, an input transmission line, a first output transmission line with a first movable cantilever and a second output transmission line with a second movable cantilever. At least part of said input transmission line, part of said first movable cantilever and part of said second movable cantilever are covered with permanent magnetic films. Magnetization of said permanent magnetic films is controlled to allow latching in one state to occur when said switch is actuated so that said first movable cantilever moves towards said input transmission line, arising from an external magnetic field. Latching between said first movable cantilever and said input transmission line occurs due to a magnetic attracting force between said permanent magnetic films in said first movable cantilever and in said input transmission line. Hence, microwaves from said input transmission line is allowed to propagate to said first output transmission line but not allowed to propagate to said second output transmission line. Latching will also occurs in another state when said switch is actuated so that said second movable cantilever moves towards said input transmission line, arising from a reversed external magnetic field. Latching between said second movable cantilever and said input transmission line occurs due to a magnetic attracting force between said permanent magnetic films in said second movable cantilever and in said input transmission line. In this case, microwave signals from said input transmission line will be allowed to propagate to said second output transmission line but will not be allowed to propagate to said first output transmission line.
In yet another embodiment, a double-throw miniature microwave switch with latching is given. Said switch consists of a dielectric substrate, an input transmission line, a first output transmission line with a first movable cantilever, a second output transmission line with a second movable cantilever and a third non-movable cantilever for latching. At least part of said input transmission line, part of said first movable cantilever, part of said second movable cantilever and part of said third non-movable cantilever are covered with permanent magnetic films. Magnetization of said permanent magnetic films is controlled to allow latching in one state to occur when said switch is actuated so that said first movable cantilever moves towards said input transmission line, arising from an external magnetic field. Latching between said first movable cantilever and said input transmission line occurs due to a magnetic attracting force between said permanent magnetic films in said first movable cantilever and in said input transmission line. Magnetization of said permanent magnetic films is also controlled to allow latching in this state to occur when said switch is actuated so that said second movable cantilever moves towards said third non-movable cantilever, arising from said external magnetic field. Latching between said second movable cantilever and said third non-movable cantilever occurs due to a magnetic attracting force between said permanent magnetic films in said second movable cantilever and in said third non-movable cantilever. Hence, microwaves from said input transmission line is allowed to propagate to said first output transmission line but not allowed to propagate to said second output transmission line. Latching will also occurs in another state when said switch is actuated so that said first movable cantilever moves towards said third non-movable cantilever and gets latched, whereas said second movable cantilever moves towards said input transmission line and gets latched. In this case, microwave signals from said input transmission line will be allowed to propagate to said second output transmission line but will not be allowed to propagate to said first output transmission line.
In still another embodiment, a double-throw miniature microwave switch with latching mechanism and a smooth transition region is given. Said switch consists a dielectric substrate, an input transmission line with a movable cantilever, a first output transmission line and a second output transmission line with a non-movable cantilever. At least part of said movable cantilever, said non-movable cantilever and said first output transmission line are covered with permanent magnetic films. Magnetization of said permanent magnetic films is controlled to allow latching in one state to occur when said switch is actuated so that said movable cantilever moves towards said first output transmission line, arising from an external magnetic field. Latching between said movable cantilever and said first output transmission line occurs due to a magnetic attracting force between said permanent magnetic films in said movable cantilever and in said first output transmission line. Hence, microwaves from said input transmission line is allowed to propagate to said first output transmission line but not allowed to propagate to said second output transmission line connecting to said non-movable cantilever. Latching in another state will be allowed to occur when said switch is actuated so that said movable cantilever moves towards said non-movable cantilever connecting to said second output transmission line, arising from a reversed external magnetic field. Latching between said movable cantilever and said non-movable cantilever occurs due to a magnetic attracting force between said permanent magnetic films in said movable cantilever and in said non-movable cantilever connecting to said second output transmission line. In this case, microwave signals from said input transmission line will be allowed to propagate to said second output transmission line but will not be allowed to propagate to said first output transmission line. Since sharp corners in the transition region between the input transmission line and the output transmission lines are eliminated in this switch, the reflection and losses of propagating microwaves or millimeter waves are minimized.